J/AJ/147/150 Velocities of globular clusters in M104 (Dowell+, 2014)
Beyond the brim of the hat: kinematics of globular clusters out to large radii
in the Sombrero galaxy.
Dowell J.L., Rhode K.L., Bridges T.J., Zepf S.E., Gebhardt K., Freeman K.C.,
de Boer E.W.
<Astron. J., 147, 150 (2014)>
=2014AJ....147..150D 2014AJ....147..150D
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Spectroscopy ;
Radial velocities ; Photometry, UBVRI
Keywords: galaxies: elliptical and lenticular, cD - galaxies: individual: M104 -
galaxies: kinematics and dynamics - galaxies: star clusters: general
Abstract:
We have obtained radial velocity measurements for 51 new globular
clusters around the Sombrero galaxy. These measurements were obtained
using spectroscopic observations from the AAOmega spectrograph on the
Anglo-Australian Telescope and the Hydra spectrograph at WIYN.
Combining our own past measurements and velocity measurements obtained
from the literature, we have constructed a large database of radial
velocities that contains a total of 360 confirmed globular clusters.
Previous studies' analyses of the kinematics and mass profile of the
Sombrero globular cluster system have been constrained to the inner
∼9' (∼24kpc or ∼5Re), but our new measurements have increased the
radial coverage of the data, allowing us to determine the kinematic
properties of M104 out to ∼15' (∼41kpc or ∼9Re). We use our set of
radial velocities to study the GC system kinematics and to determine
the mass profile and V-band mass-to-light profile of the galaxy. We
find that M/LV increases from 4.5 at the center to a value of 20.9
at 41kpc (∼9Re or 15'), which implies that the dark matter halo
extends to the edge of our available data set. We compare our mass
profile at 20kpc (∼4Reor ∼7.4') to the mass computed from X-ray data
and find good agreement. We also use our data to look for rotation in
the globular cluster system as a whole, as well as in the red and blue
subpopulations. We find no evidence for significant rotation in any of
these samples.
Description:
Spectroscopic observations were acquired for this study during two
observing runs.
The first spectra were taken with the AAT using the AAOmega
multi-object spectrograph in 2009 May. AAOmega is fed by the 2dF fiber
positioner which contains 392 fibers. For each fiber the dual-beam
spectrograph produces both a red and a blue spectrum. For our
observations, the red arm of the spectrograph was configured with the
1000I VPH grating centered at 8580Å, resulting in spectra with a
dispersion of ∼0.54Å/pixel and a wavelength range of
∼8015-9120Å. The blue arm of the spectrograph was configured with
the 580V VPH grating centered on a wavelength of 4750Å, yielding
spectra that have a central dispersion of ∼1.04Å/pixel and a
wavelength range of ∼3680-5800Å. Targets for our observations were
selected from the photometric globular cluster (GC) system study of
Rhode et al. (2004AJ....127..302R 2004AJ....127..302R), in which 1748 candidate GCs around
M104 were identified using wide-field BVR images. From the Rhode et
al. (2004AJ....127..302R 2004AJ....127..302R) list we selected ∼500 candidates without
measured velocities and with V magnitudes between 19.0 and 22.0.
Additional globular cluster candidates were observed using the Hydra
spectrograph on the WIYN 3.5m telescope at Kitt Peak National
Observatory (KPNO) in 2011 February. Hydra is a multi-object
spectrograph with ∼85 available fibers and a one degree field of view.
Targets for the Hydra observations were selected from the remaining
unobserved objects in the Rhode et al. (2004AJ....127..302R 2004AJ....127..302R) list
described above. We restricted our target selection to only those
objects with V magnitudes brighter than 20.5. Our resulting target
list contained 72 GC candidates. For the observations, Hydra was
configured with the red fiber bundle and the 600@10.1 grating centered
at a wavelength of 5300Å, providing a spectral range that extends
from 3880 to 6710Å. This is similar to the spectral coverage of the
blue arm of the AAOmega data.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 579 Properties of the target objects with measured
velocities
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See also:
J/MNRAS/401/1965 : Globular clusters in M104 (Harris+, 2010)
J/MNRAS/376/960 : X-ray emission from the Sombrero galaxy (Li+, 2007)
J/ApJ/658/980 : New velocities for 62 M104 globular clusters
(Bridges+, 2007)
J/AJ/132/1593 : BVR photometry of NGC 4594 globular clusters
(Spitler+, 2006)
J/MNRAS/327/1116 : VI photometry of Sombrero globular clusters (Larsen+, 2001)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- r_Name Reference on Name (1)
4- 7 I4 --- Name Identifier of the globular cluster
9- 10 I2 h RAh Hour of Right Ascension (J2000)
12- 13 I2 min RAm Minute of Right Ascension (J2000)
15- 19 F5.2 s RAs Second of Right Ascension (J2000)
21 A1 --- DE- Sign of the Declination (J2000)
22- 23 I2 deg DEd Degree of Declination (J2000)
25- 26 I2 arcmin DEm Arcminute of Declination (J2000)
28- 32 F5.2 arcsec DEs Arcsecond of Declination (J2000)
34- 38 F5.2 mag Vmag ? The V band magnitude (2)
40- 43 F4.2 mag B-V ? The (B-V) color index (2)
45- 48 F4.2 mag B-R ? The (B-R) color index (2)
50- 55 F6.2 arcmin oRA [-17/19] Right Ascension offset from M104 center
57- 62 F6.2 arcmin oDE [-18/19] Declination offset from M104 center
64- 68 F5.2 arcmin Rad [0.37/25.15] Angular radius from M104 center
70- 75 F6.2 deg PA [0/360] Position angle of the globular cluster
77- 83 F7.1 km/s HRV [-233/10434] Heliocentric radial velocity
85- 89 F5.1 km/s e_HRV [4.8/203] Uncertainty in HRV
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Note (1): Whenever possible, the objects are identified using the sequence
numbers assigned by Rhode & Zepf (2004AJ....127..302R 2004AJ....127..302R; given as RZ# in the
table). In those cases where an object did not have an RZ# identifier, we
adopted the identifier number from the literature in the following order of
preference: Spitler et al. 2006 (cat. J/AJ/132/1593; S#), Larsen et al.
(2002AJ....124..828L 2002AJ....124..828L; C-# or H2-#), and Bridges et al.
(1997MNRAS.284..376B 1997MNRAS.284..376B; 1-# or 2-#).
Note (2): Photometric data provided in this table is a compilation of data from
the literature, and is not available for every source.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 07-Oct-2014